I finally rooted with unrevoked3 and installed a rooted version of the standard HTC rom.
The procedure is quite simple. Here it is (in detail). Obviously at your own risk…
Download unrevoked3 from http://unrevoked.com/
Launch reflash (I used the linux version). The phone reboots and now has an additional application that gives root rights to applications that request it.
Install the “Rom Manager” from the market.
Download a ROM to replace the one on the phone, copy it to the SD card.
I took Official_FroYo_Market_fixed.zip which is available on
http://forum.xda-developers.com/showthread.php?t=741775
and I also downloaded
[http://android.adamg.co.uk/bravo/radio/32.43.00.32U\_5.09.00.20.zip](http://android.adamg.co.uk/bravo/radio/32.43.00.32 U_5.09.00.20.zip)
for the “rom radio” (no idea what it is, but before I upgraded it too, everything worked except the video…)
Launch the ROM manager and install the “Official_FroYo_Market_fixed.zip” rom by making a backup. The ROM manager will first download something else, this is normal.
After reboot, launch the ROM manager and install “32.43.00.32U_5.09.00.20.zip”, without backup this time, since we have already done it.
There you go, after this last reboot, you have a rooted Froyo.
I tested for 1 hour, and it works.
For your information, I had the Swisscom hotline for a long time on Wednesday. The person I spoke to assured me that the warranty remains valid for the hardware (however, they did not guarantee anything for the software aspects and compatibility with their network).
I told him that I would refer to this discussion in the event of a problem, so that he had to be sure, and he confirmed, adding that if I had it repaired, I could indicate that I had changed the ROM and it should not be touched (!)